Sway bar Q...2mm difference?

[schubee]

I was wondering if there is a significant difference in handling of upgrading sway bars by 2mm. The stock sway bar size on my car is 20mm front and 18mm rear. If I swap to 22mm fronts and 20mm rears, will I notice any difference on the track? I acquired this set from an RSA.

[masraum]

Yep, that'll make a difference. The outside of the torsion bars and swaybars are what do most of the work which is why drilled torsion bars work.

[BGCarrera32]

Try this, unhook your sway bars and go for a drive. Pretty dramatic diff. So it is conceivable that you would notice a 2mm diff. I upgraded my Carrera from 20/18 to 22/21, quite noticeable...

-BG

[1fastredsc]

Don't remember the details, but in my suspension book that i read, for every unit increase in diameter the torsional value increase exponentially. Although i can't remember off the top of my head whether it was cubed or squared. Either way each incriment that's increased is a big difference.

[masraum]

Here, this doesn't exactly relate to our cars, but it does show the difference when small changes are made.

http://www.tsimportedautomotive.com/Swabarra.html

[surflvr911sc]

I noticed a big but reasonable difference when I went w/ 22/21 bars on my SC.

[Chuck Moreland]

Originally posted by 1fastredsc
Don't remember the details, but in my suspension book that i read, for every unit increase in diameter the torsional value increase exponentially. Although i can't remember off the top of my head whether it was cubed or squared. Either way each incriment that's increased is a big difference.

Stiffness of a torsion bar increases with the 4th power of the diameter! So small size changes make dramatic spring rate changes.

Spring Rate = (D^4) X (Spring constant)

Going from 20mm to 22mm yields a 46% increase in stiffness, for a 10% increase in diameter.

[1fastredsc]

[schubee]

Wow, thanks for the replies. I'll definitely be under my car tonight doing this r&r!

Thanks again!

[surflvr911sc]

Originally posted by Chuck Moreland
Stiffness of a torsion bar increases with the 4th power of the diameter! So small size changes make dramatic spring rate changes.

Spring Rate = (D^4) X (Spring constant)

Going from 20mm to 22mm yields a 46% increase in stiffness, for a 10% increase in diameter.

Chuck, is this same w/ a sway bar? I assume it would be but does the length have any effect on it?

I would probably answer my own question if I just did the math.

[1fastredsc]

Longer length decreases it, but not at the same rate that a larger diamter increases it. Also, with sways that have bends at the end (like factory i believe) as opposed to splined lever arms, the bends produce a little of there own spring effect. That i do remember from that book, i should scan the formula portion of that chapter, really interesting.